Franchitti, of Chip Ganassi Racing, busted past pole-sitter Will Power after a restart on the fifth lap and never looked back, turning in a dominating performance in the season-opening IndyCar event.
He was out of the top only during his two pit stops, finishing 7.2 seconds ahead of Team Penske's Power.
Tony Kanaan of KV Racing Technology-Lotus came in third, holding off a hard-charging Simona de Silvestro down the stretch.
De Silvestro, meanwhile, notched a career-best fourth-place finish and Takuma Sato rounded out the top five finishers.
Swim Week Miami Beach 2014 [PHOTOS]